1. Field of the Invention
This invention relates to a four-unit type zoom lens, and particularly to a compact zoom lens having a zoom ratio of the order of six times and suitable for a single-lens reflex camera, a video camera or an electronic still camera.
2. Related Background Art
As a zoom lens in which the focal length at the wide angle end is shorter than the diagonal line of the picture plane and which has a zoom ratio as high as three or more times, there is well known a four-unit zoom lens comprising a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power.
Such zoom lenses are proposed in Japanese Patent Publication No. 61-55093, Japanese Laid-Open Patent Application No. 58-127908, U.S. Pat. No. 4,789,226, etc.
However, the zoom lenses disclosed in these publications are of relatively high variable power, but the full length of the lens, the diameter of the fore lens and the amount of movement of each lens unit for zooming are great, and these zoom lenses could not be said to minimize these and obtain a high performance.